Electric discharge tube



Sept. 13, 1932. R. LOWIT ELECTRIC DISCHARGETUBE Filed Jan. 19, 1928 I NV EN TOR: R L owzlt 7mm M/hla A TTORNEYS.

Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE BUDOLI 155m, 0]nnaLm-nmnsnn, om, ASSIGNOB IO DEUTSCHE GLUE- ]ADENIABBII RICH. IUBTZ &DB. IHG. PAUL SCHWABZKOPI' G. I. B. E OF BERLIN- EALENBEE, emm

ELECTRIC DISCHARGE TUBE Application fled Iannary 19, 1928, Serial No.

This invention relates to an electric rectifier having one or moreanodes and an incandescent cathode, which emit a sufiicient stream ofelectrons at a comparatively low temperature, which is substantiallybelow the disintegration temperature and consequently the melting point.

The object of the invention is to provide rectifiers w'th cathodes ofthe character above referred to which will be capable of being used forhigher voltages or currents, or both, than has hitherto been possible.By means of the rectifier constructed according to the invention, it ispossible to rectify alternating currents of any desired frequency evenwhen the maximum voltage of 250 volts is reached or exceeded, it beingossible to control voltages which are even h1gher than a multiple of2,500 volts. It is also possible to use the recti-' fier according tothe present invention for controlling currents of many amperes which wasnot hitherto possible to control with rectifiers having a solid cathodeenclosed in a glass vessel.

It has already been proposed to construct rectifiers with a cathode ofpure tungsten and a filling of inert gases, the pressure of the gasbeing greater than 1 mm. column of mercury. However, it has not beenpossible to control by means of such rectifiers voltages and currentshaving the maximum value which can be obtained by the rectifieraccording to the present invention.

Corresponding to the low pressure also the gas filling will require asmaller amount of gas and consequently there will be a saving in thevery expensive gas, such as ar 11, neon and helium. If use is madeinstea of such a rare gas, of nitrogen or metal vapours, the advantagesconcerning the saving in expenditure are, it is true, less important.However, the smaller gas content is also connected with a smaller heatconductivity and consequently the transfer of heat from the incandescentcathode to the vessel of the rectifier, which is preferably made ofquartz, glass or the like, is reduced. In consequence thereof also, thesurface of this vessel which radiates the heat can be made smallerwithout its reaching inadmissible high temperatures. This leads 248,017,and in Germany January 20, 1827.

follows that for the same output the leading in wires for the heatingcurrent required for the incandescent cathode can also be of smalldiameter; and vice versa if the said leads are not altered, it ispossible to control substantially greater emissions of electrons andtherefore larger currents which have to be rectified.

Further, the surprising result has been as certained that in s ite ofthe use of such a low pressure for t e same output the temperature ofincandescence can be further reduced, whereby the life of the cathode issubstantially increased. One of the reasons therefor may consist in thisthat owing to the reduction of the gas content by the reduction inpressure and by reducin the size of the vessel also the number 0 gasions which impinge upon a cathode of given surface and which, on the onehand have an ad-- ditional disintegrating efiect and, on the other hand,a neutralizing effect upon the electrons, is reduced.

This advantage is especially noticeable in the case of incandescentcathodes made of a primary material which is capable of greaterdisintegration at the same temperature as compared with pure tungsten,such as for instance, molybdenum and also in the case of such cathodes,which contain an additional substance such as thorium and uraniumcapable of facilitating the emission of electrons, such material beingactive on the outer surface of the cathode and capable-of being split bythe gas ions impinging thereon.

The molybdenum used as base metal allows the incorporation of morethorium oxide than e. g. tungsten without losing ductility even if beingcold. Furthermore, such molybdenum in the form of a wire can be wound innarrow coils even if it has-a quite large diameter and therefore anemitting surface larger than a tungsten wire. Lastly, by the molybdenumacting as a catalyst on the thorium oxide the reactivation of thecathode during operation is assured because substantially reducedthorium-oxide, i. e. metallic thorium is now difiunding from the innerof the body of-the cathode to its outer surface and there replacing anythorium which has disappeared by splitting or evaporation.

A further advantage of the invention lies in this that with a givenvoltage the electrodes can be arranged nearer to one another than in thecase of a higher gas pressure as hitherto used; vice versa, with a givendistance between the electrodes higher Volta es can be controlled. Thisalso explains w y it is possible to use a rectifier according to thepresent invention in connection with high voltages which were hithertoimposslble to control by means of glass vessel rectifiers.

Whatever may be the nature of the inert gas with which the vessel isfilled the said gas always contains impurities because it is only in thelaboratory and not in large works that use is made of methods forpurifying the gas. It therefore follows that when the pressure andconsequently the amount of filled gas is reduced also the amount ofimpurities introduced into the vessel with the gas is also reduced.Further, as has already been pointed out above the actual contents ofthe vessel can be reduced also with a given voltage or current or outputand consequently the amount of impurities that can be introduced isfurther reduced. However, these impurities, according to the presentscientific knowledge, constituted one of the reasons which reduced thelife of the incandescent cathode since, during the operation these tweenelectrodes of the same polarity, that is to say anodes, had to bemaintained in order to avoid direct leakage between these electrodes,without reaching the cathode. By the amount of'impurities being reduced,according to the invention also the possibility of a direct leakage isreduced and this explains why in a rectifier according to the inventionthe distance between the electrodes and consequently also the dimensionsof the narrator vessel and more particularly its gas contents can befurther reduced.

The accompan ing drawing is a diagrammatical section t rough a rectifieraccording to the invention. The invention is of course not limited tothe sketch shown.

1 is a glass bulb or vessel with a so-called plug 2 provided with a footcontact 3 and also screw contact 4 and further two looplike terminals 5and 6, these contacts or terminals bein insulated from each other by theglass of t e plug 2.

In the vessel'l is arranged a cathode 7 of a homogeneous molybdenum wirecontaining thorium, thorium oxide or both in an amount from .25 up to10%. This cathode is connected at its ends by leading-in wires 8 and 9respectively with the contacts 4 and 3 respectively. Anodes 10 and 11respectively are arranged on op osite sides to the helically woundcathode and connected with the leading-in wires 12 and 13 respectivelywith the terminals 5 and 6 respectively. The vessel is first evacuatedand the electrodes are, if needed,-freed from occluded gases, whereupona filling of inert or rare gases 1s introduced at a pressure of about 3to 30 millimeters. 1

The anodes may be made of any material which, when the surface by whichthe current enters is properly dimensioned is not disintegrated by theheating up which is unavoidable. More particularly the anode may be madeof tantalum, tungsten, molybdenum, nickel, graphite and even iron.

With these as primary material, thorium, thorium oxide or other metalsand metalloids which are difi'erent from the primary material, areemployed as the additional substance and also to cathodes in which amixture of the mentioned primary substances is employed .with anadditional substance or a mixture of additional substances. Withtungsten as primary substance for the cathode, 0.25 to 10% of thorium isa suitable addition. 7 y

A rectifier according to the present invention.is manufactured in thesame way as other electric vacuum vessels filled with gas or metalvapours at a lower pressure than 30 mm. mercury column. First of all thevessel is deprived as much as possible of occluded gases and adheringwater vapour by heating, and is thereupon actuated as much as possible,whilst the gases are'removed from the electrodes. The'inert gas or metalvapour or a mixture thereof is thereupon introduced into the vesseluntil it reaches the pressure lower than 30 mm. mercury column requiredaccording to the present invention, whereupon the vessel is removed fromthe pump and is sealed up.

The discharge vessel or rectifier may be constructed in any known orsuitable manner,

more particularly the vessel, if intended for 1 a rectifier, may be madetubular, the cathode being arranged at one end and the anode at theother end, or, the cathode may be arranged in the centre and one anodeat each end. When the construction embodies two or more anodes a centralpart ma be provided for the reception of the cat ode onto which areformed a number of preferably bent arms corresponding to the number ofanodes, the latter being built-inin the proximit of the end of thecorresponding arm.

at I claim is 1. An electric rectifier comprising an electric dischargevessel having an anode, a cathode of molybdenum and an addition of from0.25% to 10% thorium oxide, the molybdenum acting as a catalyst on thethorium oxide to reduce the same to metallic state, and a filling ofinert gas in said vessel at a pressure from about 3 mm. up to about 30mm. mercury column.

2. An electric rectifier comprising an electric discharge vessel havingan anode, a cathode of molybdenum and an addition of from 0.25% to 10%thorium, in metallic state, and a filling of inert gas in said vessel ata pressure from about 3 m. up to about 30 mm. mercury column.

In testimony whereof I have signed my name to this specification.

RUDOLF LOWIT.

